To answer your question, yes you can but not sure you can do it over the phone. You can, or I did, buy a State Park Pass for all Texas parks there at the office. You can then call them the day before you go and they will give you the combination for the lock at the gate. Don't know if you can register over the phone but worth a try. The gate opens at 7am and the office opens at 8am. It's the safest and best ramps on the lake and kept very clean. Hope this helps.
"Sometimes there just aren't enough rocks"